One 'L' of a lens that will not let you down!

I recently upgraded my digital camera to the Canon 20D and decided I could not insult it by plonking my Sigma 18-50mm DG lens on the front. Very little point in having an 8.2MP sensor and shoving cheap grade glass in front that doesn't have the resolving power to cope!

So, after years of jealously coveting an L series lens, I took the plunge and bought this Canon 17-40mm wide angle USM lens. Boy what a difference! It may be one of the cheaper L series lenses but it carries the name with pride and does its title justice. I use a film body for slides as well as my 20D digital so this lens does different things for me. On my film body it is a super-wide angle 17mm lens that produces stunning landscapes. Using that end of the range for buildings and tilting the camera up at all will give you steeply converging verticals but you really shouldn't need to do that anyway!

On my 20D, the 1.6 multiplication factor comes into play due to the APS sized sensor. That means the effective focal length is 27mm-64mm so is an excellent 'standard' lens with a decent enough wide angle to be useful. If you want super wide at this level, you will have to buy the 10-22mm EF-S lens but this only works on the 20D and the 300 or 350D so don't buy it for the 10D!

Chromatic aberation (colour fringing in areas of high contrast) and spherical aberation (distortion at edges of the picture) are virtually non-existent due to the ultra-low dispersion lenses. This gives beautifully sharp images with the USM autofocusing responding quickly and accurately. Allied to this is the curved diaphragm elements which give must smoother background blurring. This is sometimes referred to as the 'bokeh' (Japanese word for blur!) and is better because there are few or no angles for light to cause distortion when using wide apertures to get shallow depth of field and focusing all the attention on the sharply focused subject while allowing it to sit forward from its surroundings by way of the blurring.

The lens does not have a macro facility but don't let that put you off as it focuses closer than you might expect. It has a 28cm close-focusing distance but remember this is to the film plane. You have about 13 centimetres from the film/sensor plane to the front of the lens and thus you can get your lens to about 15 cms (6 inches) and get perfectly sharp pictures.

A lot has been said about the lens hood which is the size of a small dinner plate! It is a bit of a pain if you have a small camera bag but it is definitely useful and does make a real difference when used with the sun close to the front of the camera.

The 77mm filter thread does mean filters are a bit expensive compared to 58mm lenses that many of us use. However, shop around and you can find them at good prices and without any question you will want to have a UV filter on the front. It would be maniacal to pay this much for a lens and then to afford it no protection from an accidental scratch! One hint, Hama or a lot cheaper than Hoya and perfectly good enough.

Overall, this is the lens I have yearned for over the years and now I have one I won't be buying anything other than L series in the future (with the possible exception of a Sigma EX lens as they are also top notch and a bit cheaper so a useful fall back) so hands off, this is mine! :o)